Heavy crude oil is found in many parts of the world and often represents substantial volumes of energy resources. Some examples are: Orinoco basin in Venezuela, oilfields in Colombia, tar sands in Canada and numerous other smaller oilfields in the world. Generally, these crudes are highly viscous, bituminous materials of heterogeneous chemical and physical composition.
Heavy crude is difficult to transport as a liquid and many technologies and processes have been developed and deployed over many decades to overcome these difficulties and upgrade heavy crudes. Typically these technologies and processes involve three approaches that are sometimes used in combination:                Use of heat (typically steam) to partially melt the crude, reduce viscosity to a transportable material;        Use of surfactants and water to make a hydrocarbon-water emulsion that lowers the viscosity to that of a transportable material; and        Use of a light hydrocarbon diluent (typically naphtha or light crude) that is mixed with the heavy crude, to provide a diluted stream having lower viscosity enabling transport, and the light hydrocarbon diluent (DIL) is then recovered at the refinery and returned for reuse or is processed along with the heavy crude.        
A large amount of information regarding these technologies exists. That mass of information notwithstanding, these technologies suffer from drawbacks and inadequacies that can be related to infrastructure availability, energy requirements and economics, need for further separations and processing at refineries etc.
The use of hydrocarbon diluents, referred to in the art as “DIL”, technology is widely practiced in Venezuela, Colombia and other Latin American countries with heavy crude fields that are located in remote areas. Typically, the Heavy Crude (HVC) to DIL ratio is about 80:20 by volume to enable viscosity reduction to provide a transportable condition. With bitumen, the amount of DIL can be about 50% by volume. Hence, a very large volume of the DIL has to be transported and brought onto the field by a pipeline or other transport such as trucks, and then the mixture has to be transported back through the pipeline or back by trucks. Furthermore, this mixture has to be separated and/or processed at the refinery. Thus, any substantial reduction in volume of the DIL required to process the HVC and similar dense crudes can provide enormous benefits.
In the nomenclature of this art, a “dilbit” is a bitumen diluted with one or more lighter petroleum hydrocarbon products, typically natural-gas condensates such as naphtha. Diluting bitumen makes it much easier to transport, for example in pipelines. According to the Alberta Oil Sands Bitumen Valuation Methodology, 2008-9995, Calgary, Alberta, Canadian Association of Petroleum Producers, December 2008, “Dilbit Blends” means “blends made from heavy crudes and/or bitumens and a diluent, usually natural-gas condensate, for the purpose of meeting pipeline viscosity and density specifications, where the density of the diluent included in the blend is less than 800 kg/m3.” A similar definition of “dilbit” is “bitumen that has been reduced in viscosity through addition of a diluent . . . such as condensate or naphtha” [Canada's Oil Sands: Opportunities and Challenges to 2015 (Energy Market Assessment), Calgary, Alberta, National Energy Board:115-118 (May 2004)].
The latter source defines “condensate” as “a mixture comprised mainly of pentanes and heavier hydrocarbons recovered as a liquid from field separators, scrubbers or other gathering facilities or at the inlet of a natural gas processing plant before the gas is processed.” A “diluent” is there defined as “any lighter hydrocarbon, usually pentanes plus, added to heavy crude oil or bitumen in order to facilitate its transport on crude oil pipelines.”
Two further definitions include “synbit” as “a blend of bitumen and synthetic crude oil that has similar properties to medium sour crude,” and “synthetic crude oil is a mixture of hydrocarbons generally similar to light sweet crude oil, derived by upgrading crude bitumen or heavy crude oil.” [Canada's Oil Sands: Opportunities and Challenges to 2015 (Energy Market Assessment), Calgary, Alberta, National Energy Board:115-118 (May 2004).]
If the diluent density is greater than or equal to 800 kg/m3, the diluent is typically synthetic crude and accordingly the blend is called “synbit” [Canada's Oil Sands: Opportunities and Challenges to 2015 (Energy Market Assessment), Calgary, Alberta, National Energy Board:115-118 (May 2004)].
In locations other than Canada, light crude oils from natural reservoirs or naphtha are used as diluents.